This invention relates to a method of controlling a compressor, especially a vehicle air conditioning compressor, and to a device for practicing the method.
In general, air conditioning operations for a vehicle interior are carried out in a temperature reducing mode, in which the temperature of the vehicle interior is decreased; and in a temperature maintenance mode, in which the temperature inside the vehicle is maintained at a comfortably low value. In the temperature reducing mode effected during initial operation, a high air conditioning capability is required, but in the temperature maintenance mode, such a high air conditioning capability is not required. Heretofore, in many cases, a compressor having a capacity as large as permitted by the capacity of the engine was installed on the vehicle in order to achieve the air conditioning operation quickly. Therefore, when the compressor was run steadily in the temperature maintenance mode, the capability of the compressor was excessively high with respect to the air conditioning load, and therefore the compressor was in a low load air conditioning operation. Accordingly, the compressor was operated with a low volumetric efficiency and the on-off frequency of the clutch interposed between the compressor and the engine was increased. Therefore, the clutch was liable to be quickly worn, and since a large start torque is produced whenever the on-off operation of the clutch is carried out, the operator feels uncomfortable while he drives the vehicle.
On the other hand, at the start of the compressor, liquid compression is sometimes cured. The liquid compression is a serious problem for a compressor in which the quantity of discharge per revolution at the start is large and a sufficiently large discharge chamber volume is not provided. The liquid compression greatly reduces the durability of the compressor, and sometimes produces loud noises. Some higher quality vehicles employ a system in which the compressor is operated with the EPR (evaporator pressure regulator) cycle providing a constant evaporation pressure, and when the refrigerant is overcooled it is blown off after being heated to the optimum temperature. However, this system is not economical in many aspects.